Cast iron material, seal material and the production method

ABSTRACT

A floating sealing ring formed from a seal material composed of C, Si, Mn, Ni, Cr and the rest composed of Fe and inevitable impurities, wherein contents of said C, Si, Mn, Ni and Cr with respect to the entire cast iron material are C: 2.9 to 3.8 wt %, Si: 1.0 to 2.5 wt %, Mn: 0 to 0.8 wt % (note that 0 is not included), Ni: 3.5 to 5.0 wt %, and Cr: 2.6 to 5.5 wt %.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application, which claims the benefit of pendingU.S. patent application Ser. No. 11/062,868, filed Feb. 23, 2005. Thedisclosure of the prior application is hereby incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cast iron material, a seal materialfor a floating seal, and the production method, and particularly relatesto a cast iron material and a seal ring material for a floating seal ofconstruction machines and vehicles, having high hardness, excellentwear-and-abrasive resistance, and the production method.

2. Description of the Related Art

A floating seal apparatus is used as a seal for track rollers ofconstruction machines and vehicles, to prevent dirt from intruding intothe rollers and to prevent inner lubricating oil from leaking to theoutside. A floating seal apparatus comprises a pair of floating sealrings on a stationary side and a rotatable side and is installed arounda shaft in a state of not contacting the shaft, that is, in a state offloating from the shaft. Also, the floating seal rings on the stationaryside and rotatable side respectively have a sliding surface facing toeach other for mutually contacting by sliding and are used in a state offacing to each other via the sliding surfaces.

The respective floating seal rings on the stationary side and therotatable side are incorporated respectively in a mechanism on thestationary side and a mechanism on the rotatable side via O-rings, andboth of the floating seal rings are pressured to contact by an elasticforce of the O-rings via the sliding surfaces. Accordingly, it ispossible to seal between the mechanism on the stationary side and themechanism on the rotatable side regardless of whether it is rotating ornot rotating and to prevent intrusion of muddy water, earth and sand,etc. to inside the roller and leakage of lubricating oil to the outside.

A material composing a floating seal ring as above is required to havehigh hardness, excellent wear-and-abrasive resistance, etc., and castiron, etc. produced by a casting method has been conventionally used. Ascast iron as such, for example, high-chromium cast iron,chrome-molybdenum cast iron and nickel-chrome cast iron, etc. are used(for example, the Japanese Unexamined Patent Publications No. 6-109141and No. 6-114538).

High-chrome cast iron and chrome-molybdenum cast iron are materialshaving high hardness. Particularly, chrome-molybdenum cast iron havingapproximately the same structure with that of high-chrome cast iron andhaving a Mo content of 2 to 4 wt % has high hardness as 64 or so in HRC.However, high-chrome cast iron and chrome-molybdenum cast iron aresubjected to thermal treatment of hardening, etc. for obtaining highhardness, and a large internal load is imposed on the material itself bythe thermal treatment, so that it is liable that the physical strengthbecomes very brittle.

As nickel-chrome cast iron, for example, Ni-hard cast iron, etc. may bementioned. Ni-hard cast iron has a Ni content of 3.5 to 5.0 wt % or soand has martensitic matrix, and the wear resistance is excellent.However, similar to the above high-chrome cast iron, Ni-hard cast ironis also subjected to thermal treatment of low temperature annealing,etc. for improving the toughness and wear resistance, so that althoughhigh-toughness is attained, the physical strength is liable to becomevery brittle.

Also, the Japanese Unexamined Patent Publication No. 2002-098236discloses a floating seal ring using a sintered alloy produced by apowder metallurgical method as a constituent material. Such a floatingseal ring produced by a sintered alloy has a high degree of freedom in amaterial composition comparing with a floating seal ring made by castiron produced by the above casting method, therefore, there is anadvantage of being excellent in dimensional precision. Also, a physicalproperty of a sintered alloy produced by a powder metallurgical methoddepends on the material composition, so that it is necessary to adjustthe material composition to change a physical property of the sinteredalloy. However, an improvement of a physical property is limited only byadjusting the material composition, and wear resistance and otherproperties are insufficient when using a sintered alloy as a materialfor forming a floating seal ring.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a cast iron materialhaving high hardness, excellent wear-and-abrasive resistance, a floatingseal and other seal materials formed by the cast iron material, and theproduction method.

The present inventors found that the above object can be attained bymaking a content of elements other than Cr in a cast iron material usedfor a seal material for a floating seal, approximately as same as thatin the above Ni-hard cast iron and setting a Cr content to 2.6 to 5.5 wt% with respect to the entire cast iron, and completed the presentinvention.

Namely, according to the present invention, there is provided a castiron material composed of C, Si, Mn, Ni, Cr and the rest composed of Feand inevitable impurities, wherein

contents of the C, Si, Mn, Ni and Cr with respect to the entire castiron material are

C: 2.9 to 3.8 wt %,

Si: 1.0 to 2.5 wt %,

Mn: 0 to 0.8 wt % (note that 0 is not included),

Ni: 3.5 to 5.0 wt %, and

Cr: 2.6 to 5.5 wt %.

In the cast iron material according to the present invention,preferably, contents of P and S in the inevitable impurities withrespect to the entire cast iron material are P: 0.5 wt % or less and S:0.5 wt % or less.

P is compounded with iron to form steadite (Fe₃P), which results in atendency of declining a cutting property of cast iron and making castiron brittle. S makes a coagulation point of the cast iron high, whichresults in a tendency of deteriorating a flow property of molten metaland making cast iron after casting brittle. Therefore, the smaller acontent of P and S is in inevitable impurities in cast iron, the better.

In the cast iron material according to the present invention,preferably, a matrix structure is a structure selected from perlite,bainite and martensite, or a mixed structure of these, and has a finestructure consisting of dendritic cementite and carbides of Cr.

In the present invention, the matrix structure is more preferably amixed structure, wherein martensite is the main body, and furthermorepreferably a mixed structure of perlite and martensite, whereinmartensite is the main body.

In the cast iron material according to the present invention,preferably, hardness of the cast iron material is 62 or higher, morepreferably 65 or higher in HRC.

A seal material of the present invention is formed by any one of theabove explained cast iron materials. The seal material is notparticularly limited and, for example, a mechanical seal and floatingseal, etc. may be mentioned and, particularly, a floating seal for trackrollers is preferable.

Since a floating seal ring of the present invention is formed by theabove seal material and has high hardness, excellent wear resistance andcorrosion resistance, it is preferable to be used as a seal for trackrollers of construction machines and vehicles.

According to the present invention, there is provided a productionmethod of a seal material, including steps of casting in a mold a moltenmetal composed of C, Si, Mn, Ni, Cr and the rest composed of Fe andinevitable impurities, and curing by cooling, wherein

contents of the C, Si, Mn, Ni and Cr with respect to the entire moltenmetal are

C: 2.9 to 3.8 wt %,

Si: 1.0 to 2.5 wt %,

Mn: 0 to 0.8 wt % (note that 0 is not included),

Ni: 3.5 to 5.0 wt %, and

Cr: 2.6 to 5.5 wt %;

wherein a cooling rate at a position of a sliding surface of the sealmaterial is higher than that on other parts when curing by cooling.

In a production method of the seal material of the present invention,molten metal is made to be in a composition range of the presentinvention and a sliding surface position to be a seal surface isforcibly and preferentially cooled at a higher cooling rate comparingwith that on other parts, so that it is possible to form a finestructure on the sliding surface and, particularly, it is possible toimprove hardness and wear resistance of the sliding surface. Also, as afine structure, a structure, wherein dendritic cementite and finecarbides mainly including Cr are dispersed and the matrix structure isselected from perlite, bainite and martensite or a mixed structure ofthese, is preferable.

In the production method of the seal material according to the presentinvention, preferably, contents of P and S in the inevitable impuritieswith respect to the entire cast iron material are P: 0.5 wt % or lessand S: 0.5 wt % or less.

In the production method of the seal material according to the presentinvention, when the cooling rate (° C./min.) at the sliding surfaceposition of the above seal material is C_(R)1 and the cooling rate (°C./min.) on other parts is C_(R)2, preferably, 1≦C_(R)1/C_(R)2≦2.5.

Alternately, in the production method of the seal material according tothe present invention, preferably, the cooling rate at the time ofcooling and curing the sliding surface position is preferably 300 to700° C./min., and more preferably 500 to 700° C./min.

According to the present invention, as a result that a componentcomposition composing a cast iron material is made to be in the abovepredetermined range, that is, a content of elements other than Cr isapproximately as same as that in Ni-hard cast iron and a Cr content ismade to be 2.6 to 5.5 wt % with respect to the entire cast iron, it ispossible to provide a cast iron material having high hardness, excellentwear-and-abrasive resistance. Also, by using the cast iron material ofthe present invention as a material composing a seal material, it ispossible to provide a floating seal and other seal materials having theabove properties.

Furthermore, according to a production method of a seal material of thepresent invention, molten metal is made to be in a composition range ofthe present invention, and a sliding surface position to be a sealsurface of a seal material is forcibly and preferentially cooled at ahigher cooling rate comparing with that on other parts, so that it ispossible to form a fine structure on the sliding surface, andparticularly, it is possible to provide a floating seal and other sealmaterials having high hardness, excellent wear-and-abrasive resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, embodiments of the present invention will be explained in detailbased on drawings, in which:

FIG. 1 is a sectional view of a floating seal apparatus according to anembodiment of the present invention;

FIG. 2A and FIG. 2B are views of surface roughness of a worn state aftera wear resistance test on a sliding surface of samples of an example anda comparative example of the present invention; and

FIG. 3A and FIG. 3B are views of a moving amount on the insidecircumferential side of a seal band after a wear resistance test onsamples of an example and a comparative example of the present invention

DESCRIPTION OF THE PREFERRED EMBODIMENT

Floating Seal Apparatus 1

As shown in FIG. 1, a floating seal apparatus 1 according to anembodiment of the present invention comprises a floating seal ring 2 onthe stationary side and a floating seal ring 7 on the rotatable side,made to be a pair. The floating seal rings are installed around a shaft20 in a state of not contacting the shaft 20, that is, in a state offloating from the shaft 20.

The floating seal ring 2 on the stationary side is combined with astationary housing 12 via an O-ring 18, and the floating seal ring 7 onthe rotatable side is combined with a rotatable housing 15 via an O-ring19.

The floating seal ring 2 on the stationary side has a ring structurehaving a larger inner diameter than an outer diameter of the shaft 20,and a groove 3 of a predetermined depth is provided on the outercircumferential surface. On a bottom surface of the groove 3 is formed ataper surface 4 gradually getting closer to the shaft 20 as it getsfarther from the floating seal ring 7 on the rotatable side.

Similarly, the floating seal ring 7 on the rotatable side has a ringstructure having a larger inner diameter than an outer diameter of theshaft 20, and a groove 8 of a predetermined depth is provided on theouter circumferential surface. The groove 8 is formed with a tapersurface 9.

The floating seal ring 2 on the stationary side and the floating sealring 7 on the rotatable side respectively have a sliding surface 5 and asliding surface 10 on its outer circumference part on the facingsurfaces, and both of the floating seal rings face to each other via thesliding surface 5 and the sliding surface 10.

Also, on a surface of the floating seal ring 2 on the stationary sidefacing to the floating seal ring 7 on the rotatable side, a part on aninner circumferential side continuing to the sliding surface 5 is formedwith a taper surface 6 gradually getting farther from the floating sealring 7 on the rotatable side as it gets closer to the shaft 20.

Similarly, on a surface of the floating seal ring 7 on the rotatableside facing to the floating seal ring 2 on the stationary side, a parton an inner circumferential side continuing to the sliding surface 10 isformed with a taper surface 11.

The stationary housing 12 is fixed to one end portion of the shaft 20and surrounds by its inner circumferential surface an outercircumferential surface of the floating seal ring 2 on the stationaryside. The inner circumferential surface of the stationary housing 12 isprovided with a groove 13 having a predetermined depth, and the groove13 is formed with a taper surface 14 slanting to the same direction asthat of the bottom surface of the groove 3 on the outer circumferentialsurface of the floating seal ring 2 on the stationary side.

The rotatable housing 15 is provided to be able to freely rotate on theother end portion of the shaft 20 via a shaft bearing (not shown) andsurrounds by its inner circumferential surface the outer circumferentialsurface of the floating seal ring 7 on the rotatable side. On the innercircumferential surface of the rotatable housing 15 is provided with agroove 16 having a predetermined depth over the entire circumference,and the groove 16 is formed with a taper surface 17 slanting to the samedirection of that of the bottom surface of the groove 8 on the outercircumferential surface of the floating seal ring 7 on the rotatableside.

Also, the floating seal ring 2 on the stationary side and the stationaryhousing 12, and the floating seal ring 7 on the rotatable side and therotatable housing 15 are combined respectively via the O-ring 18 and theO-ring 19, and the O-rings 18 and 19 are formed by an elastic material.It is configured that, due to an elastic force of the O-rings 18 and 19,the floating seal ring 2 on the stationary side and the floating sealring 7 on the rotatable side are pressured to contact via the slidingsurface 5 and the sliding surface 10, and between the sliding surfaces 5and 10 is sealed regardless of whether the rotatable housing 15 isrotating or not rotating.

Stationary Side and Rotatable Side Floating Seal Rings 2 and 7

The floating seal ring 2 on the stationary side and the floating sealring 7 on the rotatable side are formed by a cast iron material of thepresent invention.

The cast iron material of the present invention is composed of C(carbon), Si (silicon), Mn (manganese), Ni (nickel), Cr (chrome) and therest composed of Fe (iron) and inevitable impurities.

C (carbon) is capable of controlling an amount of carbide, such ascementite forming the chill structure, by changing the content. Also, Chas an effect of accelerating dendritic crystallization of crystalgrains and adjusting a base material structure. A content of C is 2.5 to4.0 wt %, preferably 2.9 to 3.8 wt %, and more preferably 3.2 to 3.7 wt% with respect to the entire cast iron material. When the C content istoo small, a content of cementite in the fine structure becomes smalland wear resistance and machinability of the base material tend todecline. When the content is too large, cementite in the chill structurebecomes coarse and cavities due to remelting are easily caused in thefine structure, furthermore, an amount of graphite increases andstrength of cast iron tends to decline.

Si (silicon) has an effect of extricating carbon from pig iron andaccelerating graphitization of cast iron after casting, while, has aneffect of causing dendritic crystallization or columnar crystallizationof crystal grains. A content of Si is 1.0 to 3.0 wt %, preferably 1.5 to2.5 wt %, and more preferably 2.0 to 2.5 wt % with respect to the entirecast iron material. When the Si content is too small, there is atendency that curing of the base material is not accelerated and thebase material itself becomes fine to remarkably decline machinability,while when the content is too large, it is liable that extrication ofcarbon proceeds excessively and the toughness declines.

Mn (manganese) is compounded with S (sulfur) to form manganese sulfideand has an effect of suppressing an adverse effect caused by mixing of Sinto cast iron, an effect of making the structure fine, an effect ofgraphitization caused by adding Ni to improve the matrix. A content ofMn is preferably 0 to 0.8 wt % (note that 0 is not included) withrespect to the entire cast iron. When the Mn content is too large, thereis a tendency that the structure is made noticeably fine, cast ironbecomes brittle and the machinability declines.

Since Ni (nickel) does not form carbide in cast iron, there are effectsof accelerating graphitization, suppressing arising of white pig iron,and homogenizing the structure and hardness. A content of Ni is 3.5 to5.5 wt %, preferably 4.0 to 5.0 wt %, and more preferably 4.2 to 4.5 wt% with respect to the entire cast iron material. Particularly, bysetting the Ni content to be within the above ranges, the matrix canbecome martensitic. When the Ni content becomes too small, it is liablethat the above effects cannot be obtained, while when the content is toolarge, it is liable that residual austenite in the matrix becomesbainitic and strength of the cast iron declines.

Cr (chrome) forms fine carbide having high hardness and has an effect ofimproving wear resistance and matrix strength. A content of Cr is 2.0 to6.5 wt %, preferably 2.5 to 6.0 wt %, and more preferably 2.6 to 5.5 wt% with respect to the entire cast iron material. When the Cr content isset to be 2.0 wt % or more, preferably 2.5 wt % or more, and morepreferably 2.6 wt % or more, it becomes possible to bring carbide of Crinto a solid-solution on cementite. Particularly, when the cementitehaving the solid solution of carbide of Cr is combined with martensiticmatrix, an effect of improving hardness of cast iron can be obtained.When the Cr content is too small, it is liable that the above effectcannot be obtained, while when the content is too large, it is liablethat hardness when the base material is separated from the mold becomestoo high, machinability is deteriorated, and cutting becomes difficult.

In the present invention, particularly by setting the Ni content to bein the above ranges, matrix of the cast iron material can becomemartensitic. As a result that the matrix becomes martensitic, the castiron material can be made highly strong. On the other hand, Ni also hasan effect of accelerating graphitization. Therefore, when the Ni contentis too large, an amount of graphitized carbon becomes too large, andstrength of the cast iron material tends to decline.

Thus, in the present invention, by furthermore adding a predeterminedamount of Cr as above, Cr and carbon are compounded to form carbide ofCr. Therefore, since carbon can be made to be carbide of Cr by addingCr, an increase of a graphite amount (graphitization of carbon) causedby adding Ni can be suppressed. At the same time, by adding apredetermined amount of Cr as above, fine and highly hard carbide isformed, so that wear resistance can be improved. Particularly, as aresult that the carbide of Cr is brought into a solid-solution oncementite, and the cementite with the solid solution of Cr is combinedwith the martensitic matrix, hardness of the cast iron can be improved.

Furthermore, while it will be explained in detail later on, by setting acomponent composition of the cast iron to be within a predeterminedrange as above, and forcibly and preferentially cooling the slidingsurfaces 5 and 10 at a higher cooling rate than that on other parts atthe time of cooling and curing a molten metal in the production process,the cast iron structure on the sliding surfaces can be made fine, andhardness and wear resistance of the sliding surfaces can be particularlyimproved.

As the above inevitable impurities, for example, P (phosphor) and S(sulfur), etc. are mentioned, and the smaller a content of theinevitable impurities is, the more preferable.

P is compounded with iron to form steadite (Fe₃P) and has a tendency ofdecreasing cutting property of the cast iron and making the cast ironbrittle. Accordingly, the smaller a content of P is, the morepreferable; and the content is 0.5 wt % or less, more preferably 0.3 wt% or less with respect to the entire cast iron material.

S has a tendency to heighten a coagulation point of the cast iron,deteriorate a flow property of a molten metal and make the cast ironbrittle. Therefore, the smaller a content of S is, the more preferable;and the content is 0.5 wt % or less, more preferably 0.1 wt % or less,furthermore preferably 0.05 wt % or less, and particularly preferably0.02 wt % or less with respect to the entire cast iron material.

In the present embodiment, the cast iron material of the presentinvention is used as a material of forming the floating seal rings 2 and7 on the stationary side and rotatable side, so that it is possible toheighten the hardness. The hardness of the floating seal rings can bepreferably 62 or more, more preferably 64 or more, and furthermorepreferably 65 or more in the Rockwell hardness HRC.

Production Method of Floating Seal Rings 2 and 7 on Stationary Side andRotatable Side

The floating seal rings 2 and 7 on the stationary side and the rotatableside composing the floating seal apparatus 1 of the present embodimentare produced by preparing raw materials to form cast iron, melting thesame to molten metal, and cooling and curing the molten metal in a mold.

First, raw materials are prepared, so that a composition of the castiron after casting becomes the above composition, and the raw materialsare melt in a melting furnace, etc. to obtain a molten metal. The rawmaterials are not particularly limited and coke, pig iron and alloyiron, etc. may be mentioned.

Next, the thus obtained molten metal is cast in a mold, then, cooled tobe cured in the mold, and a floating seal ring formed by a cast ironmaterial is obtained. In the present embodiment, at the time of coolingand curing the molten metal in the mold, it is preferable to use a moldconfigured that sliding surfaces 5 and 10 to be seal surfaces areforcibly and preferentially cooled at a higher cooling rate comparingwith that on other parts, and a position of the sliding surfaces ispreferentially cooled comparing with other parts. As a method offorcibly and preferentially cooling the sliding surface position in themold, for example, a method of flowing a coolant to near the slidingsurface position for cooling, a mold casting method, and centrifugalcasting method, etc. may be mentioned.

By using a mold as above and forcibly and preferentially cooling thesliding surfaces 5 and 10 at a higher cooling rate comparing with thaton other parts, a fine structure can be formed on the sliding surface ofthe floating seal ring. As such a fine structure, a structure whereindendritic cementite and fine carbides mainly containing Cr are dispersedand the matrix structure is selected from perlite, bainite andmartensite or a mixed structure of these, is preferable.

The cooling rate at the time of cooling and curing as above is, forexample, when the cooling rate (° C./min.) at the sliding surfaceposition of the above seal material is C_(R)1 and the cooling rate (°C./min.) on other parts is C_(R)2, preferably 1≦C_(R)1/C_(R)2≦2.5, morepreferably 1≦C_(R)1/C_(R)2≦2.0, and furthermore preferably1<C_(R)1/C_(R)2≦2.0.

Alternately, the cooling rate of the sliding surfaces 5 and 10 ispreferably 300 to 700° C./min., and more preferably 500 to 700° C./min.When the cooling rate is too slow or too fast, it is liable that thefine structure explained above is hard to be formed, so that the coolingrate is preferably within the above ranges.

Note that, in the present embodiment, it is significant that the finestructure explained above is formed on the sliding surfaces 5 and 10under the above cooling condition, therefore, it is sufficient if thecooling under the above condition is performed at 400 to 500° C. or so,which is a temperature that the fine structure is formed. Namely, thecooling condition after forming the fine structure on the slidingsurfaces 5 and 10 is not particularly limited and may be suitablyselected.

In the present embodiment, by forming the fine structure, whereindendritic cementite and fine carbides mainly containing Cr aredispersed, on the sliding surface under the above cooling condition,strength and hardness of the cast iron can be improved. Particularly, asa result that fine cementite and fine carbides mainly containing Cr areformed, abrasion wear caused by a loss of coarse cementite and brittlestructure, for example as exhibited in white pig iron, can beeffectively prevented.

Also, when the matrix structure of the above fine structure is made tobe preferably a mixed structure of perlite, bainite and martensite, morepreferably a mixed structure chiefly consisting martensite, andfurthermore preferably a mixed structure of perlite and martensite,wherein martensite is the main body, matrix hardness can be improved.

Note that, in the present embodiment, formation of the above finestructure on the sliding surface can be attained by making a componentcomposition of the cast iron to be the composition of the presentinvention. Particularly, by controlling an adding amount of Ni and Cr,depth of chill on the chill structure forming the fine structure can bestabilized.

The floating seal apparatus 1 comprising the floating seal rings 2 and 7on the stationary side and the rotatable side of the present inventionproduced by the above explained process has high hardness and excellentwear resistance and can be suitably used as a seal for track rollers ofconstruction machines and vehicles.

Note that the present invention is not limited to the above embodimentsand variously modified within the scope of the present invention.

For example, in the above embodiments, a floating seal was taken as anexample of a seal material according to the present invention, but theseal material according to the present invention is not limited to thefloating seal and may be any seal material as far as it is formed bycast iron material having the above composition.

Example

Below, the present invention will be explained based on furthermoredetailed examples, but the present invention is not limited to theseexamples.

First, raw materials were prepared so that respective componentcompositions shown in Table 1 are obtained, thermal treatment (heatingmelting) at 1600° C. was performed on the raw materials, and the resultwas cooled at a cooling rate of 500° C./min. to obtain samples 1 to 5 ofa cast iron material. Also, chrome-molybdenum cast metal was prepared asa sample 6, and three kinds of Ni-hard cast metals were prepared assamples 7 to 9.

Next, measurement of Rockwell hardness, a wear resistance test andcorrosion resistance test were made on the respective cast iron materialsamples.

Measurement of Rockwell hardness was made on sliding surfaces of castiron material samples 1 to 9 by making a shape of the samples a sealsize shape having an outer diameter ø of 90.1 mm and using a Rockwellhardness testing machine. The measurement results are shown in Table 1.

The wear resistance test was conducted by preparing a stationary testpiece in a seal size shape having an outer diameter ø of 90.1 mm and arotatable test piece in the same shape by using the samples 1 and 6 andproducing a floating seal apparatus as shown in FIG. 1. Here, thestationary test piece corresponds to the floating seal ring 2 on thestationary side, and the rotatable test piece corresponds to thefloating seal ring 7 on the rotatable side. The test atmosphere was amixture of 84 wt % of mud (Arizona test Dust) and 14 wt % of water onthe outer circumferential side of the stationary test piece androtatable test piece and lubricating oil on the inner circumferentialside. The test condition was to rotate the rotatable test piece at 200rpm under a condition of “rotating in the forward direction for 20seconds, posing for 20 seconds, rotating in the backward direction for20 seconds, and posing for 20 seconds”, which was assumed to be onecycle, and the total was 10000 cycles. A worn state of sliding surfacesof the samples 1 and 6 after the wear resistance test is shown in FIG.2, and a moving amount on the inner circumferential side of the sealband after the wear resistance test is shown in FIG. 3.

The corrosion test was conducted on the samples 1, 6 and 9 by using atest piece in a seal size shape having an outer diameter ø of 90.1 mmand using a salt spray testing device. The test condition was to washthe seal surface with acetone first, then, the testing atmosphere was asaltwater concentration of 5 wt %, a pH of 6.5 to 7.2, a temperature of35° C. and humidity of 95 to 98%, and the testing time was one hour.After spraying saltwater, the test piece was washed with an alkalisolution, furthermore, washed away with nonionic water to removeexcessive corrosive, then, corrosion percentage on the seal surface wasevaluated.

TABLE 1 Cast Iron Material Sample Component Composition (wt %) No. C SiMn Cr Ni Mo V P S Structure HRC 1 Example 3.64 2.20 0.44 5.18 4.68 0.000.00 0.08 0.01 Martensitic Matrix Fine 67 Structure on Perlite Matrix 2Example 3.68 2.04 0.35 4.02 4.43 0.00 0.00 0.28 0.01 Martensitic MatrixFine 65 Structure on Perlite Matrix 3 Example 3.61 2.50 0.35 4.95 4.490.00 0.00 0.29 0.01 Martensitic Matrix Fine 66 Structure on PerliteMatrix 3-1 Example 3.40 2.00 0.30~ 3.00 4.50 0.00 0.00 0.30 0.01Martensitic Matrix Chill 63 0.80 Structure on Perlite Matrix 4Comparative 3.30 2.15 0.79 1.02 0.00 2.30 1.40 0.00 0.01 MartensiticMatrix Chill 64 Example Structure on Perlite Matrix 5 Comparative 3.102.25 0.79 0.54 0.00 0.00 0.00 0.00 0.00 Martensitic Matrix Chill 47Example Structure on Perlite Matrix 6 Comparative 2.90~ 0.70~ 0.30~15.0~ 1.00 or 2.00~ 2.00 or 0.00 0.00 Martensitic Matrix Chill 60Example 3.80 1.40 0.80 18.0 less 4.00 less Structure on Perlite Matrix 7Comparative 3.00~ 0.40~ 0.30~ 1.20~ 3.50~ 0.40 or 0.30~ 0.30 or 0.10 orMartensitic Matrix Chill 57~64 Example 3.60 1.00 0.90 1.70 4.30 less0.90 less less Structure on Perlite Matrix 8 Comparative 3.15~ 1.00~0.30~ 1.40~ 3.30~ 0.00 0.00 0.30 or 0.15 or Martensitic Matrix Chill 56Example 3.35 1.20 0.80 2.50 3.80 less less Structure on Perlite Matrix 9Comparative 2.90~ 2.00~ 0.80 or 0.20 or 4.00~ 0.00 0.00 0.10~ 0.15 orMartensitic Matrix Chill 60 Example 3.80 2.50 less less 5.00 0.50 lessStructure on Perlite Matrix Note that the rest of the componentcomposition is Fe.

Evaluation 1

Table 1 shows a component composition, cast iron metal structure andRockwell hardness of each of the samples 1 to 9. Note that the cast ironmetal structure was determined by observing the surface of the cast ironmaterial by using a metal microscope.

From Table 1, the example samples 1 to 3-1 of the present invention hada component composition forming the cast iron material of within therange of the present invention, and the surface structure of the castiron material was formed by martensitic matrix fine structure on perlitematrix, so that the surface hardness resulted in being high as 67, 65,66 and 65 in HRC, respectively. On the other hand, in the samples 4 to 9as comparative examples, wherein the component composition was out ofthe range of the present invention, the surface structure of the castiron material became a martensitic matrix chill structure on perlitematrix, and the surface hardness became low as 47 to 64 in HRC,respectively.

From the result, it was confirmed that, by setting the componentcomposition forming the cast iron to be in the range of the presentinvention and preferably forming a fine structure, a cast iron materialhaving high hardness and excellent wear resistance could be obtained.

Evaluation 2

FIG. 2A and FIG. 2B are views of surface roughness of a worn state onthe sliding surface of the samples 1 and 6 after the wear resistancetest, wherein FIG. 2A is a view of surface roughness of the sample 1 andFIG. 2B is a view of surface roughness of the sample 6. As is obviousfrom the drawings, although both of the samples 1 and 6 were much wornon the outer circumferential side for directly contacting watercontaining mud, it was confirmed that a worn amount was smaller and thewear resistance was superior in the sample 1 when comparing the sample 1with the sample 6. Accordingly, it was confirmed that by setting thecomponent composition forming the cast iron to be in the range of thepresent invention and, preferably, making the cast iron structure to bea fine structure, it is possible to obtain a cast iron material havinghigh hardness and excellent wear resistance.

Also, FIG. 3A and FIG. 3B are views of a moving amount on the innercircumferential side of the seal band of the sample 1 and sample 6 afterthe wear resistance test, wherein FIG. 3A is a view of a moving amounton the inner circumferential side of the sample 1 and FIG. 3B is a viewof a moving amount on the inner circumferential side of the sample 6.From the drawings, it can be confirmed that the sample 1 had a smallermoving amount on the inner circumferential side of the seal band whencomparing the sample 1 with the sample 6 both on the stationary side andthe rotatable side. Note that the moving amount on the innercircumferential side of the sample 1 was 0.28 mm on the stationary sideand 0.86 mm on the rotatable side, and that of the sample 6 was 0.44 mmon the stationary side and 1.28 mm on the rotatable side. Accordingly,it was confirmed that by setting the component composition forming thecast iron to be in the range of the present invention, it is possible tomake the moving amount on the inner circumferential side of the sealband smaller, so that the cast iron material of the present inventionwas suitable as a cast iron material for a floating seal ring.

Evaluation 3

As a result of conducting the corrosion test, the example sample 1 had acorrosion percentage of 7%, and the comparative example samples 6 and 9had corrosion percentages of 9% and 13%, respectively. Therefore, theexample sample 1 was confirmed to have superior corrosion resistance tothat of the sample 6 as chrome-molybdenum cast iron including arelatively large amount of Cr. Accordingly, it was confirmed from theresult that, by making the component composition composing the cast ironto be in the range of the present invention, it is possible to obtain acast iron material having superior corrosion resistance comparing withthe related art.

1. A floating sealing ring formed from a seal material composed of C,Si, Mn, Ni, Cr and the rest composed of Fe and inevitable impurities,wherein contents of said C, Si, Mn, Ni and Cr with respect to the entirecast iron material are C: 2.9 to 3.8 wt %, Si: 1.0 to 2.5 wt %, Mn: 0 to0.8 wt % (note that 0 is not included), Ni: 3.5 to 5.0 wt %, and Cr: 2.6to 5.5 wt %.
 2. The floating sealing ring according to claim 1, whereinon a sliding surface of said floating seal ring is formed a structure,wherein a matrix structure is selected from perlite, bainite andmartensite or a mixed structure of these, and a fine structureconsisting of dendritic cementite and carbides of Cr is included.